This invention relates to means for and methods of tempering composite fiber panels without requiring a bake oven for the tempering process.
As used herein, the term xe2x80x9cdryerxe2x80x9d is interchangeable with the term xe2x80x9ccatalyst.xe2x80x9d The term dryer is an historic word for a catalyst used with industrial agricultural oils in the paint and coating industry. The dryers are actually added to these oils in order to catalyze the oxidation reaction thereof. The three main types of catalyst used with this invention are:
1. Many metal dryers commonly used in he oil based paint and coating industry, some of which are manganese, iron, cobalt, zirconium, calcium, and rare earth.
2. Resins and modified resins, some of which include low molecular MDI (isocyanate resin) phenolformaydehyde resin, and ureaformaldehyde resins. Also, some of these resins are available in blended form, such as the ESL, Kelvin, Drisoy, and Beckosol materials.
3. Organic peroxide materials are various peroxides carried in a solvent carrier, which actually add oxygen to the oil and, hence, a rapidly progressing oxidation reaction. The most common peroxide used in MEKP, methyl ethyl ketone peroxide.
Composite panels are usually made of wood, agriculture or other fibers by a manufacturing process leading to a production of panels in the form of hardboard, oriented strand board, fiber board siding, wafer board, medium density fiber board, particle board, and other similar boards. Wood is the preferred fiber. The panels or boards are made by mixing fiber and a binder and then placing the mixture in a hot press.
Wood-fiber based composites are sensitive to moisture, particularly moisture in a liquid form. In addition to linear expansion and thickness swell, moisture can cause blistering and fiber-pop at the panel surface. Since fiberboard is often painted or coated, especially for decorative use, blistering and fiber-pop become important issues, especially when using water based topcoats or adhesives. Tempering also provides a strong surface layer that gives added strength, especially to doorskins used in the manufacturing of doors.
During building construction or transport of the finished composite, structural panels are often exposed to weather elements before they are protected by a siding or roofing. Severe weather can cause water damage to unprotected panels in a very short period of time. To protect the paneling during the construction process, a tempering topcoat can be applied to the panel""s surfaces to provide them with a hard, moisture resistant surface.
Usually, the process of manufacturing these composite panels includes a use of a tempering oil which is applied to the surfaces of the panel in order to impart a smooth, strong, and water resistant surface thereto. However, to date, the manufacturing technology has required a high temperature bake oven in order to cure the tempering oil after it has been applied to the surface of the panel.
In the following description, reference is made to a number of tempering oil additives which may be further identified in the following manner. xe2x80x9cAlincoxe2x80x9d is a term of art which is well known in the oil industry. A letter after xe2x80x9cAlincoxe2x80x9d indicates the viscosity of the oil. xe2x80x9cArcher 1xe2x80x9d is a trademark and xe2x80x9cGP1125xe2x80x9d, xe2x80x9cScientific Double Boiled Linseed Oilxe2x80x9d and xe2x80x9cML189xe2x80x9d are the manufacturer""s product codes of the Archer Daniels Midland Company of Decatur, Ill. xe2x80x9cBeckosolxe2x80x9d, xe2x80x9cDressyxe2x80x9d, xe2x80x9cEsskolxe2x80x9d, xe2x80x9cKellinxe2x80x9d, and xe2x80x9cKelsolxe2x80x9d are product lines of the Richol Corporation. xe2x80x9cMondurxe2x80x9d is a product of the Bayer Corporation. The letters or numbers following these names are the manufacturer""s product codes. The value xe2x80x9cpxe2x80x9d refers to the results of a statistical analysis of at least two blends. When xe2x80x9cp less than 0.5xe2x80x9d, it means that there is a statistically significant difference between the two blends without reference to whether the difference is good or bad.
Reference is made to U.S. Pat. Nos. 5,607,633 and 5,719,304 which describe systems for bonding wood or other agriculture based fibers in order to form composite panels. These patents provide a binder made from drying oils having more than one carbon-to-carbon double bond, usually separated by a methylene blend, commonly described as xe2x80x9cmethyline interruptedxe2x80x9d. These patents teach a shifting or relocation of the methylene blend in order to remove the interruption and, thereby, produce a conjugated oil. Then, the drying oil is mixed with a bonding agent. This form of conjugated drying oil is sold under the trademark xe2x80x9cArcher 1xe2x80x9d by the Archer Daniels Midland Company of Decatur, Ill.
Other examples of tempering oils are linseed oil, soy bean oil, canola oil, sunflower oil, tung oil or mixtures thereof. Also, other materials, such as metal catalysts (manganese, cobalt, iron, zirconium, rare earth, etc.), organic catalysts (such as organic peroxides), phenolic resins, isocyanate resins, ureaformaldehyde resins, and melamine resins can be added to the tempering oils to produce different effects, as desired. The manufacturer describes two of the preferred oils in the following manner.
The Manganese (xe2x80x9cMnxe2x80x9d) dryer used with the various oils had 40% wt. solids and was supplied by the OMG Chemicals Company, which uses the product code FOA #910 for identification purposes. The percentage of the added Mn dryer was based on the liquid weight of the drying oil that was used.
Heretofore, the tempering drying oils have usually been baked on the panel in a high temperature oven, which may produce a Hazardous Air Pollutant (xe2x80x9cHAPxe2x80x9d) or a concentration of Volatile Organic Compounds (xe2x80x9cVOCxe2x80x9d), both of which may become a serious pollutant. As a result, governmental regulations (e.g., the EPA Clean Air Act) severely limit the release of VOC""s, HAP""s, and other pollutants. Other problems caused by VOC""s and HAP""s are found, especially in hot press areas and bake oven areas. For example, the VOC fumes may lead to fire hazards, especially in exhaust flues and stacks.
Still another problem in the production of composite panels is the very high cost resulting from the energy consumption required to heat the bake ovens. These costs tend to be increased sharply by such things as weather conditions, political instability in countries where fuel is produced, and other unpredictable events.
Accordingly, to provide stable manufacturing costs and practices, a cleaner environment and the like, a desirable advance in the art results from an elimination of bake ovens in the panel tempering process.
Therefore, in keeping with an aspect of the invention, a mixture of a tempering oil in combination either with a catalyst dryer or a low molecular weight isocyanate resin, or other resins with a fast curing characteristic and with a minimal amount of hazardous emissions, is sprayed on one or both surfaces of a composite panel. After the composite panels are sprayed, they are stacked inside a curing chamber or on a pile for a period of time required to cure the oil. The duration of the time period depends, at least in part, on whether the oil is sprayed on the panel while it is still hot, for example, immediately after it is out of the press which formed it, or whether it is sprayed after the panel has been sanded. After an optimal and prescribed period of time, the panels are removed from the curing chamber and found to have a tempered surface which at least equals or exceeds the properties of temperatured surfaces produced by most prior methods that utilized a bake oven.
More particularly, an evaluation of the inventive process began with a study of various linseed oil based tempering agents, as follows:
The GP1125 linseed oil was selected as a base because it is refined to minimize low molecular weight compounds which tend to flash off at high temperatures.
Tempered composite panels are submitted to the following tests in order to evaluate their quality and other desirable characteristics.
A cobb-ring test is carried out by gluing a ring on a surface of the tempered composite panel. Then, the panel is carefully weighed with the ring in place. Next, a prescribed amount of water is placed in the ring and the panel is left with the water standing in the ring for a prescribed period of time, for example. Often, cobb-ring tests are carried out by using a 2-inch diameter ring with 55 grams of water setting in the ring during a 24-hour period. Then, the water is poured off and the panel is again weighed. The difference in weight between the two weighings is an indication of how much water has penetrated the tempered surface and is absorbed into the panel. Usually, the test result is expressed as a percentage of the dry weight which has been added to the panel and which appears after the test.
A tape-pull test is carried out by first placing and pressing an adhesive tape on the tempered surface of the panel. Thereafter, the tape is ripped off the surface. Next, the adhesive surface of the tape is inspected to determine how much fiber has been ripped from the surface of the tempered panel.
A cleavage test is provided by a block that is glued to the face of the panel having the tempering oil coating thereon. After the glue has fully set, the block is put into a clamp and the panel is ripped off the block. The amount of force required to rip the panel off the block is an indication of the rupture strength of the tempered panel.